1. Field of the Invention
The present invention relates to a disk unit which performs the writing and reading of data to and from a medium in the form of a disk, a yoke built into this disk unit and a process of manufacturing this yoke.
2. Description of the Related Art
A disk unit comprises a spindle motor which supports and rotates a medium in the form of a disk (hereinafter referred to simply as a disk), a head which performs the writing and reading of data to and from the disk, a suspension arm which is provided, at its leading end, with the head and which causes the head to be opposed to a desired track on the disk by oscillating the head, a bearing which oscillatably supports the suspension arm, and a voice coil motor to oscillate the suspension arm.
As a voice coil motor, one which is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-325507, for example, is known. This voice coil motor has a coil which is integrally attached to a bearing which supports a suspension arm, a magnet to generate a magnetic field in the coil, a top yoke to which the magnet is bonded, and a bottom yoke opposed to the top yoke in such a positional relation that the coil is sandwiched between the bottom yoke and the magnet.
Thus, by causing a driving current to flow through the coil, an electromagnetic force is generated and the suspension arm is oscillated so that the head is opposed to a desired track on the disk.
However, the above-described conventional voice coil motor had the problem that a leakage flux through the yoke occurs. That is, when the yoke is made thin for miniaturization and weight reduction of the disk unit, magnetic saturation occurs in the yoke, generating an undesirable leakage flux. When a leakage flux is generated, undesirable magnetic fields are generated inside and outside the unit, thus posing the problem that irregularities such as noise occur.
Although it is, therefore, conceivable to increase the yoke thickness in the direction of the magnetic flux of magnet, the yoke becomes heavy, and this idea is inconsistent with weight reduction. Furthermore, attaching a plate piece or the like, as a separate body, to the yoke in order to increase the thickness, poses the problem that the manufacturing cost increases.